The field is two-stroke cycle opposed-piston engines. More specifically the application relates to a low reactivity, compression-ignition (LRCI), opposed-piston engine.
A compression-ignition engine for a vehicle is an internal combustion engine in which the heat of compressed air ignites fuel injected into, and mixed with, the air as it is compressed. A two-stroke cycle engine is a type of compression-ignition engine that completes a power cycle with a single complete rotation of a crankshaft and two strokes of a piston connected to the crankshaft. An opposed-piston engine is a two-stroke cycle, compression-ignition, internal combustion engine in which two pistons are disposed in opposition in the bore of a cylinder for reciprocating movement in opposing directions. The cylinder has longitudinally-spaced inlet and exhaust ports that are located near respective ends of the cylinder. Each of the opposed pistons controls one of the ports, opening the port as it moves to a bottom center (BC) location, and closing the port as it moves from BC toward a top center (TC) location. One of the ports provides passage for the products of combustion out of the bore, the other serves to admit charge air into the bore; these are respectively termed the “exhaust” and “intake” ports. In a uniflow-scavenged opposed-piston engine, charge air enters a cylinder through its intake port as exhaust gas flows out of its exhaust port, thus gas flows through the cylinder in a single direction (“uniflow”)—from intake port to exhaust port.
Air and exhaust products flow through the cylinder via an air handling system. Fuel is delivered by injection from a fuel delivery system. As the engine cycles, a control mechanization including an engine control unit (ECU) and associated sensors and actuators governs combustion by operating the air handling and fuel delivery systems in response to engine operating conditions. The air handling system may be equipped with an exhaust gas recirculation system to reduce undesirable compounds produced by combustion.
The continuous drive to reduce emissions and fuel consumption of internal combustion engines is pushing the exploration of new combustion regimes for existing engine types. Autoignition of low reactivity fuels, such as gasoline, has been tested in four-stroke internal combustion engines. When a low reactivity fuel is utilized in a compression-ignition engine without a spark plug for igniting the fuel, lower NOx and reduced particulate matter (“PM”) after-treatment can be realized in comparison to an internal combustion, compression-ignition engine using a high reactivity fuel such as diesel.
If a low reactivity fuel were to be utilized in a two-stroke cycle, compression-ignition, opposed-piston engine, even further reductions in emissions as well as improved fuel consumption efficiencies could be realized. The inherent advantage of the opposed-piston engine of surface-area-to-volume ratio provides lower fuel consumption while reducing emissions without the need for expensive after-treatments. Thus, it is a desirable objective to equip a two-stroke, compression-ignition, opposed piston engine for operation with a low reactivity fuel such as gasoline that will self-ignite in varying engine operating conditions without ignition assistance.